Aim To explore amplitude and latency-check size function in multiple sclerosis (MS) patients without optic neuritis history. Methods Thirty-six MS patients and 21 control subjects were included. Pattern visual evoked responses to ive check sizes (2°, 1°, 30', 15', and 7') were recorded. Results P100 amplitudes were signiicantly reduced in 2°, 1° and 7' checks and, P100 latencies were signiicantly delayed in all checks in MS patients (p less 0.05). Inter-ocular amplitude/ latency differences were signiicantly higher in MS patients than control group (p less 0.05). The P100 amplitudes for 2°check was somewhat higher than amplitudes for 1° check in MS and control groups. However, MS patients had latter amplitude-check size function curve in large checks. In small checks, the slope of the amplitude-check size curves were similar for MS and control groups. The lattening of amplitude-check size function curve in large checks increased in MS patients with reduced P100 amplitudes. The P100 amplitudes for 2° check was lower than P100 amplitudes for 1° check in MS patients with reduced P100 amplitudes in contrast to normal subjects and MS patients with normal P100 amplitudes. Both groups had almost parallel P100 latency-check size curves in all checks. With respect to 95% conidence limit in control subjects in each check sizes, the number of eyes with delayed latency and reduced amplitude in MS patients were higher in large checks. Conclusion This study showed that P100 amplitudes are reduced in MS patients without optic neuritis history, and responses to large checks are affected more than small checks.